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Overview
LG Motion
Limited recently designed and supplied a large custom built
X-Z detector positioning system for the I24 Microfocus
Macromolecular Crystallography (MX) beamline at Diamond
Light Source, the UK’s national synchrotron science
facility.
Minuscule protein crystal samples are
illuminated with I24’s intense X-ray beam and the detectors
are positioned to a precision of just a few tens of microns
to capture scattered light that reveals the complexities of
protein structure and their functions.
The newly commissioned I24 beamline is used
by chemists and structural biologists for cutting-edge
molecular level studies in genomics, immune systems and
membrane proteins, and ground-breaking research in drug
design that combats major disease and viruses.
Objectives
The design specification called for the
ability to load the positioning rig with multiple detectors
up to 280 kg mass with a volume of around 1 m3 over a 1.55
metre horizontal and 0.85 metre vertical travel range to
allow increased flexibility and research throughput on the
I24 beamline. At acceptance testing, the system was actually
loaded with 420 kg -1.5 times the rated load - and
positioning repeatability for both axes was measured to
better than 10 microns which is well inside the desired
specification for the I24 detector.
Products Used
 LG Motion’s
custom-built detector positioning system is based around
Schneeberger MONORAIL AMS series linear motion guide
bearings with magnetised track linear encoders built into
the rails. This compact and durable bearing support and
fully LG Motion design and supply custom-built 2 axis
precision positioning system for 280 kg detectors on Diamond
Light Source protected incremental position measurement
system is used extensively on large scale precision machine
applications with advantages of ‘close to load’ measurement
and simplified installation plus cost benefits over
separately supplied bearings and encoders.
Two AMS bearing rails are fixed to a
large 3000 x 1000 mm horizontal base plate that is bolted to the experiment
hutch floor with provision for alignment, levelling and grouting on
installation. Each horizontal rail has three bearing carriages that support the
upper moving horizontal stage carriage plate which is approximately 1000 mm
square and 20 mm in thickness.
The 280 kg detector load is evenly
distributed on the horizontal stage carriage plate using a welded steel
framework with four vertical linear bearing rails which allow the vertical
translation of the detector mounting platform which is fabricated from MiniTec
ProfileSystem machine framing components. With one pair of bearing rails
utilising three bearing carriages and the opposing pair just one carriage, this
design is much preferred to a more conventional dual bearing arrangement with an
inherent overhung load; allowing for smaller linear bearings and simplified
power transmission mechanics to be used.
Each axis is servo motor driven with
precision ballscrews, bearing block type supports and a flexible coupling. The
vertical axis includes a safety brake and further in-line planetary gearhead
reduction to ensure that it does not back-drive under power off conditions, even
if the fail safe brake is disengaged for any reason. Both axes also include
datum and over-travel limit switches as a part of the specification.
During the design approval,
manufacture and commissioning, LG Motion worked closely with scientists and
support staff at Diamond to ensure that the detector positioning LG Motion
design and supply custom-built 2 axis precision positioning system for 280 kg
detectors on Diamond Light Source system was installed on-budget and on-time,
and fully met relevant machine directives, safety standards and performance
specifications originally required for the project. |
